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Top Forums UNIX for Advanced & Expert Users possibility to call subprocesses from ksh ?? Post 32956 by Perderabo on Wednesday 11th of December 2002 11:37:15 AM
Old 12-11-2002
You can use nohup inside a script if you want to. But I think nohup was really intended to be used from the command line.

Different versions of nohup ignore different signals. Sun actually supplies two different versions. It writes to nohup.out if it can or $HOME/nohup.out if the current directory is not writable. A script that silently invokes nohup might interfer with a user's use of nohup with both writing to the same nohup.out file.

Inside a script, ignoring signals is easy. A script can in effect nohup itself by simply using:
trap "" HUP QUIT
and there is no question about whether or not QUIT is being ignored. Want to ignore TERM too? Just use:
trap "" HUP QUIT TERM
And now you can redirect the output whereever you want leaving nohup.out available for mamual use.

In my above script, you could do:
nohup date &
but
( trap "" HUP QUIT TERM ; exec date > date.out 2>&1 ) &
pretty much does the same thing, but gives me much more control over what is happening. Remember that parentheses start a subshell, so the trap inside the subshell does not affect the outer shell.
 

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NOHUP(1)						    BSD General Commands Manual 						  NOHUP(1)

NAME
nohup -- invoke a utility immune to hangups SYNOPSIS
nohup [--] utility [arguments] DESCRIPTION
The nohup utility invokes utility with its arguments and at this time sets the signal SIGHUP to be ignored. If the standard output is a ter- minal, the standard output is appended to the file nohup.out in the current directory. If standard error is a terminal, it is directed to the same place as the standard output. Some shells may provide a builtin nohup command which is similar or identical to this utility. Consult the builtin(1) manual page. ENVIRONMENT
The following variables are utilized by nohup: HOME If the output file nohup.out cannot be created in the current directory, the nohup utility uses the directory named by HOME to create the file. PATH Used to locate the requested utility if the name contains no '/' characters. EXIT STATUS
The nohup utility exits with one of the following values: 126 The utility was found, but could not be invoked. 127 The utility could not be found or an error occurred in nohup. Otherwise, the exit status of nohup will be that of utility. SEE ALSO
builtin(1), csh(1), signal(3) STANDARDS
The nohup utility is expected to be IEEE Std 1003.2 (``POSIX.2'') compatible. BUGS
Two or more instances of nohup can append to the same file, which makes for a confusing output. BSD
July 19, 2001 BSD
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